1. Field of the Invention
The present invention generally relates to cellular wireless communications, and particularly to networks used for coupling communications signals between cellular transceivers and land line interconnection points.
2. Statement of the Prior Art
The wireless communications area of Personal Communications Services, PCS, is under development as of the filing date hereof and employs digital pulse transmission signals in one or more of its accepted formats. PCS is similar to cellular telephone networks in the use of multiple transmission cells for the wireless connection between portable transceivers and the network. There is a general need in cellular wireless communications systems to increase the call handling capacity of the networks to accommodate more callers, higher peak usage and higher data capacity. The latter goal is particularly useful to PCS, which includes more data related services than the commonly used analog cellular telephones.
A well known approach for increasing calling capacity of a cellular system is to decrease the size and range of each cell and increase the number of cells or stationary transceivers. This allows for greater reuse of the limited number of frequency channels allocated for wireless communications, because the cells or base stations are smaller and transmit with less power. Thus, another cell, located at a closer range, can reuse the same channels for additional calls without interference. The primary disadvantage in using smaller cells is the increased installation, operating and maintenance costs of the greater number of base stations.
A suggestion has been made in U.S. Pat. No. 5,381,459, to use existing cable television networks to distribute wireless communications signals between a telephone network coupling and remote transmitter receiver sites or cells. This approach couples transmission and reception signals over the coaxial cable television network in a time and frequency multiplexed manner. Such time multiplexing requires transcription of these signals at the remote transceiver sites into and from their transmission format. This increases the complexity of the remote transceivers and their associated control electronics. This, in turn, impacts the system cost of using a greater number of smaller cells.
Coaxial cable television networks suffer the additional disadvantage of substantial variation of the distribution links within even a single network, resulting in varying gain and amplification considerations. This variability in signal loss is compounded by being temperature dependent, which places an additional time variation factor on each system link. Thus, controlling transmission power level can be difficult and even critical given the desire to both provide reliable data transmission and limit the area of cell coverage to enhance frequency reuse, This further increases the cost of the numerous remote transceivers.
One format which has been applied to PCS is code division multiple access, CDMA. This method multiplexes signals over the same bandwidth and time frame by providing each call with a unique frequency coded pattern for transmitting its data. Mobile receivers, capable of deciphering the various codes, are used to separate their particular signal of interest from the various transmitted signals. The CDMA nature of the transmission signals limits the time multiplexing and frequency multiplexing techniques which may be used to distribute the signals over a coaxial cable television network to remote transceivers without the use of extensive signal format transcription electronics at the transceivers.
Accordingly, it is an object of the present invention to provide a system for coupling PCS signals over a coaxial cable television network between a telephone network interface and remote cell sites.
It is a further object of the present invention to provide such a system having adequate signal power level control to enable optimum control of transmission signal power levels at the remote antennas.
It is a still further object of the present invention to provide such a system which minimizes the size and complexity of the transceivers associated with each remote cell sites.
It is yet a further object of the present invention to provide such a system which distributes PCS signals in a CDMA format.
In one form, the present invention provides a system for transmitting telecommunications signals from a wired system to mobile receivers, comprising a signal hub means for receiving a telecommunications transmission signal for distribution to a mobile receiver and including first means for measuring a power level of the received transmission signal, a multiplicity of distributed remote antenna drivers, each having a respective antenna, a controllable amplifier adapted to couple transmission signals to the antenna and second means for measuring a signal power level of a transmission signal at the antenna, network means for coupling the transmission signal from the signal hub means to one or more remote antenna drivers, and means for determining a gain factor for each respective amplifier and thereby the transmission signal at each respective antenna in response to the measured received signal power level and the respective measured antenna signal power level.
In another form, the present invention resides in a telecommunications system having at least one signal hub coupled via a coaxial wire network to a multiplicity of distributed remote antenna drivers with each driver having a respective antenna and a controllable amplifier adapted to couple transmission signals to the antenna, in a method for controlling signal gain of the transmission signal at the remote antenna drivers, comprising receiving, at the signal hub, a telecommunications transmission signal for distribution over the network to at least one remote antenna driver, measuring a power level of the received transmission signal at the signal hub, distributing the received transmission signal driver over the network to a remote antenna and its respective amplifier and antenna, measuring an antenna signal power level of the transmission signal at the respective antenna, and determining a gain factor for the respective amplifier and thereby of the transmission signal at the respective antenna driver in response to the measured received signal power level and the measured power level of the signal at the antenna.